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Troendle/Nankervis/Porth Page 13 5/22/2003 <br />is that though this entire analysis is based on the best available data, the results are still limited <br />by these data and assumptions used. It is critical that the databases on forest cover and stand <br />description be 'vmproved. <br />Impacts of Post 1997 Management Activity on Future Water Yield <br />As noted above, Mel Mehl (Renewable Resources, USFS Region 2, Denver, CO) provided <br />information on timber harvest activity that occurred on each of the Forests in the North Platte <br />basin, by year, from 1997 to 2001. Andrew Peavy assisted in intersecting the "activities" with the <br />original forest polygon data that was delivered to us as part of the Troendle and Nankervis 2000 <br />effort. The data layers aze complex and the information will be presented in the simplest format <br />here. <br />First, the original forest stand polygon data was clipped to the watershed boundary for the North <br />Platte River (Figure 11). The detail, associated with the stand data (Figure 12) such as specie <br />composition, age class, aspect, elevation, and management class are not shown, but were used in <br />the analysis appropriately. The activity polygons were intersected with the original stand <br />polygon data and the pre-activity stand conditions determined (See Figures 13 and 14). The <br />Forests in turn, provided information on the impact of the "activity" on stand condition; or basal <br />area. In general, stands that were clear-cut were reduced from their original stand conditions to a <br />basal azea of zero. Other partial cuts, such as pre-commercial thinning, shelter wood cut, and <br />thinning, etc. reduced stand density to 60 to 70 percent of initial condition. <br />Management activities occurred on a total of 4874 acres of the nearly 1.2 million acres of NFS <br />land from 1997 to 2001 impacting an average of 975 acres each year (1128, 950, 2134, 445, and <br />218 acres were harvested in each of the 5 years from 1997 to 2001). It should be noted that the <br />treated area used in the flow change analysis is approximately 400 acres less tha.n the 4874 acres <br />identified. Some of the activity involved prescriptions on polygons that were not identified as <br />significantly forested to begin with, so no additional increase in water yield resulting from the <br />activity could be simulated. We assumed these treatments reflected restoration or sanitation <br />practices and did not involve significant changes in vegetation that could influence water yield. <br />Based on the changes in vegetation that resulted from activities on the remaining 4456 aeres, we <br />simulated an increase in flow of approximately 0.0027 area inches per year, each year, for the 5- <br />year period from 1997 to 2001. Assuming this level of activity is repetitive thru 2017, we <br />simulated that water yield on the North Platte River will be increased approximately 0.05 azea <br />inches per year by yeaz 2017, this level of harvest equates to an estimated increase in flow of <br />4600 acre-feet of water per yeaz in 2017. This increase is substantially below the 37,000 acre <br />feet of water per year that Troendle and Nankervis (2000) had estimated could be generated, in <br />the same time frame, by implementing a program to place the nearly one-half million acres of <br />NFS land classified as Suita.ble for Timber Harvest in the North Pla.tte Basin on a 120 yeaz <br />management rotation.